Modern medical X-ray imaging systems have become a valuable tool in the healthcare profession. Imaging systems such as basic X-ray, computed tomography (CT) and fluoroscopy systems which were once found only in major medical facilities have become more commonplace due to their affordable cost and compact size. Oftentimes, mobile X-ray imaging systems are utilized outside of radiology rooms because of their ability to be transported to operating rooms or other areas serving multiple purposes, thus providing instant on-the-spot X-ray imaging.
Mobile X-ray medical imaging systems often contain various mechanical members that are typically long and slender in shape. On a typical mobile C-arm X-ray medical imaging system, an X-ray source and image detector are placed in proper proximity to the patient by attaching them to the respective ends of a C-shaped member such that they are located below and above the patient. The C-arm member can then be anchored to other structures on an imaging system through a capturing clamp that can have bearings to allow the C-arm member to slide through the clamp. This one degree of freedom movement allows the user to position the X-ray source and detector more exactly relative to the patient, so as to optimize the desired images. Furthermore, various other motion subsystems can be available on the C-arm that accommodate additional degrees of freedom. For example, the C member can be allowed to twist, or slide horizontally across the patient, or slide in the direction of head to toe of the patient, or move in elevation relative to the patient. Various mechanical members are required to accomplish motions like horizontal and vertical sliding, and these members are also typically long and slender in nature.
More advanced C-arm systems provide powered motion control to assist the user in adjusting some or all of the movements necessary for optimal imaging. This motion control can be accomplished through the use of a joystick, buttons or various foot pedals, for example. During CT/3D imaging, the C-arm traverses a continuous semi-arc around the patient's body as the imaging occurs. During fluoroscopy, the C-arm moves to distinct positions around the patient's body as distinct images are obtained. A computer with imaging software can then construct the desired CT, 3D or 2D images for diagnosis. In order to produce the clearest possible images, it is important that the C-arm not vibrate during the imaging process.
All mechanical members inherently have natural mechanical resonances that will make the member oscillate when it is acted upon by an excitation that contains energy at a mechanical resonance of the member. Likewise, if the member is not acted upon by an excitation that contains energy at a mechanical resonance of the member, the member is less likely to vibrate. Since various members of the C-arm system are long and slender, they can have a tendency to vibrate back and forth when the X-ray source and detector are moving, and can continue to vibrate for a period of time after all intended movements are completed. Such vibrations are due to natural mechanical resonances in these members, the degree of spring, and the mass and moment of inertia of loads attached to the members. In mobile imaging systems, the C-arm and associated members tend to be lighter in weight and are therefore less robust than fixed systems that can aggravate the mobile system's tendency to vibrate.
Depending on various characteristics of the systems, these vibrations can oscillate at frequencies below one cycle per second and up to many tens of cycles per second, and there can be several different vibrations occurring all at once. However, the stronger and more troublesome vibrations tend to be between 0.5 and 5 cycles per second. Because vibration can cause image blur, detailed imaging requires the x-ray source to output very short high powered x-ray pulses to freeze motion, much as a pulsing strobe light freezes motion when viewed optically, (more expensive and typically impractical due to power constraints for mobile equipment), or that the C-arm member not vibrate during image capture because vibration can cause image blur. To reduce the blur associated with the unwanted oscillation, fluoroscopic users of the C-arm may have to wait for these stronger vibrations to die down after completing a powered motion before acquiring an image, or the vibrations can require an assistant to manually stop the system from vibrating. The delay in imaging can also cause additional unnecessary distress to an injured patient who must remain stationary during the imaging process and if numerous images are required, the additional imaging time and the associated distress to the patient caused by the stabilization delay can be significant.
An even more complex mobile X-ray C-arm imaging system is designed to acquire CT or 3D image information by continuously moving the X-ray source and detector about the patient in a controlled way. Such a system can use one or more degrees of freedom from the motion capabilities previously described. In this case, it is important that the motion be smooth so that the location of the X-ray source and detector is known when image data is acquired. Errors in location can result in reconstruction artifacts for the CT or 3D images. However, natural mechanical resonances as those described above, can cause unwanted vibrations to occur while the members are in motion during CT or 3D acquisition.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a method to reduce vibrations in the accelerated members of a mobile X-ray imaging system. There is also a need in the art for a mobile X-ray medical imaging system with reduced vibration in the accelerated mechanical members.